The purpose of this investigation is to obtain further information about the detailed characteristics of coronary blood flow. Velocity profile measurements will be carried out in horses at selected sites in the coronary arteries in order to study effects of both pharmacologic and physiologic perturbations. Centerline velocity waveform, flow, and pressure time history measurements will be carried out at selected sites in the coronary arteries of large dogs, calves, and horses in order to study coronary flow dynamics on a comparative basis. Shear stress determinations will be made at selected sites in the coronary arteries. These determinations will be made by using hot-film shear stress probes to carry out in vivo measurements as well as by using computer calculation methods based on measured coronary velocity or flow waveforms. The velocity measurements will be carried out using the hot-film constant temperature anemometer technique employed on Grant HL-16236. Pulsed ultrasonic doppler (PUD) velocimeter measurements and electromagnetic flow meter will also be carried out for comparison purposes, and all three techniques will be used to study on a comparative basis coronary hemodynamics in large animals.